1. Field of the Invention
The present invention relates to an apparatus and method for displaying a three-dimensional image in real time.
2. Description of the Related Art
Recently, a three-dimensional image processing technology is used in various fields such as education, training, medical treatment, and computer games. The three-dimensional image is more useful than a two-dimensional image in that it has presence feeling, real feeling, and natural feeling.
Many researches for implementing such a three-dimensional image display are currently in progress.
The three-dimensional image display requires various technologies such as input technology, processing technology, transmission technology, display technology, and software technology. Particularly, it essentially requires researches for the display technology, digital image processing technology, computer graphic technology, and human visual system.
The most fundamental method of the three-dimensional image display is based on glasses. As typical examples, there are a color separation mode, a polarized glasses mode, and a liquid crystal shutter mode. The color separation mode permits a viewer to observe images through color glasses using different light wavelengths. The polarized glasses mode is based on different light oscillation directions. The liquid crystal shutter mode permits a viewer to observe left and right images by temporally dividing the images.
The glasses-based three-dimensional image display method provides picture quality of high definition but has two drawbacks. The one drawback arises from inconvenience caused by wearing glasses and the other drawback arises in that only scenographic feeling exists in a fixed visual point. For these reasons, researches for direct three-dimensional image display without wearing glasses are currently in progress.
The direct three-dimensional image display separates left and right images without using glasses, especially separates images corresponding to left and right eyes in a particular observation position using a parallax barrier, a lenticular plate, or a fly eye lens plate.
Particularly, an integral photography mode is well known. This integral photography mode records, transmits, and regenerates three-dimensional images formed by a fly eye shaped microlens array.
In more detail, as shown in FIG. 1, a microlens array 10 having fly eye shaped microlens arrays 11 is arranged, and a number of microimages 13 of a subject entered through each microlens 11 are recorded on a printing paper in a microimage focus surface 12.
If light is illuminated at the rear of the printing paper, respective microimages 13 recorded on the printing paper progress in the same path as when the subject is taken, so that a three-dimensional image 14 is regenerated in an original subject position.
However, a comfortable viewing zone that can observe the regenerated three-dimensional image is limited to a boundary of the three-dimensional image 14.
For example, a viewing angle of a two-dimensional display based on a cathode ray tube (CRT), a plasma display panel (PDP), and a liquid crystal display (LCD) is approximate to 120 but a viewing angle of a three-dimensional display such as an integral photography is about 20° or less.
FIGS. 2a and 2b show three-dimensional images observed in a zone other than inside and outside of a viewing angle of an apparatus for displaying a three-dimensional image.
As shown in FIG. 2a, two-dimensional microimages are provided on a screen 22. The microimages are synthesized to a three-dimensional image 23 through a microlens array 21 and then regenerated. At this time, an observer 24 located within a boundary 25 of a main viewing zone 26, i.e., within a viewing angle of the apparatus for displaying a three-dimensional image can observe the regenerated three-dimensional image 23.
The viewing angle 2ω that can observe the regenerated three-dimensional image 23 is limited to the boundary of the three-dimensional image.
As shown in FIG. 2b, if an observer 27 moves out of the main viewing zone 26 marked by dotted lines, he is entering into a satellite viewing zone 29 remarked by solid lines.
The observer 27 observes a satellite image 28 in the satellite viewing zone 29. The satellite image 28 is observed within the viewing angle 2ω, as shown in FIG. 2a. 
The satellite image 28 observed in the satellite viewing zone 29 is similar to the image 23 observed in the main viewing zone of FIG. 2a. However, the satellite image 28 has a seriously distorted three-dimensional image. This is because that an angle between vertical and horizontal directions in the regenerated satellite image 28 is different from an angle of the regenerated image 23 of FIG. 2a. 
As described above, the related art apparatus for displaying a three-dimensional image has a problem in that the viewing angle that can stably observe a three-dimensional image is narrow. For this reason, another problem arises in that the apparatus for displaying a three-dimensional image is limited in its use range.